In a belt conveyor line of the type typically used for the bulk handling of raw materials, a continuously moving looped belt and its load are supported by a system of idlers. The idler system comprises idler rolls and supporting brackets, both typically fashioned from steel. Each idler roll generally comprises a roll cylinder having two end caps at each opposite end of the roll cylinder, with the cylinder freely rotating about a fixed axle, the axle being affixed at each end to a supporting bracket, and at least one internal bearing assembly positioned inside the roll cylinder to support the roll cylinder as it rotates about the fixed axle. Three idler rolls aligned end-to-end and angled in a wide “U” or trough shape and supported by brackets attached to a cradle-like frame typically comprise one idler set. The idlers are positioned in such a way as to allow the moving belt with its load to rest directly on the freely rotating rolls so that the belt can travel the entire length of the conveyor line. Idlers are often required to perform in harsh environments, such as those incident to the mining and steelmaking industries. Bulk handling operations that involve raw materials such as coal, coke, and iron ore pellets can subject idlers to excessive moisture, abrasive particulates, contaminants and corrosive chemicals. Such harsh environmental conditions can adversely affect idler components. Exposure to contaminants can cause idler roll cylinders to seize up, corrode, and/or prematurely wear out.
Idler failure is most often caused by water, waterborne contaminants, airborne contaminants and combinations thereof seeping through a circumferential gap at the end cap located at each end of a roll cylinder. The circumferential gap is created at the interface of an axle and a typically stationary outer contact seal with an aperture at the end cap through which the axle and stationary outer contact seal extend. The gap permits the roll cylinder to freely rotate about the fixed axle. Contamination infiltrating the roll via the circumferential gap can result in bearing assembly seizure or roll cylinder corrosion. In addition, the constant vibration to which idlers are often exposed increases the likelihood of contaminants working their way through the circumferential gap and infiltrating the roll. A three-roll idler set will typically have a total of six bearing assemblies, one internal bearing assembly at each end of each of the three rolls. Failure of just one bearing assembly or corrosion of just one roll cylinder can necessitate replacement of the entire idler set. Bearing failure will most often cause the roll to seize and become stationary. A conveyor belt traveling over a stationary roll eventually will wear a flat spot on the roll at the point of contact. Too many stationary rolls will cause drag on the belt, shortening its life. Idlers wear out at different rates based on the conditions to which they are exposed. In the harshest environments, idlers might have to be replaced as often as every four months, while in benign environments, idlers might in rare instances last for up to twenty years.
The two outer rolls of an idler set, called the wing rolls, are known to fail at a rate significantly greater than the center roll, due to the greater exposure of the wing rolls to the environment, in contrast to the protection afforded to the center roll by the conveyor belt overhead. Thus, the need to mitigate/eliminate infiltration by contaminants is especially critical for the wing rolls, with the outboard end of each wing roll having the greatest environmental exposure.
Mitigating and/or eliminating contamination from infiltrating and fouling idler rolls by use of a cost-effective seal will permit increased efficiency in bearing assembly operation, extend idler life, reduce roll failures, improve conveyor belt life, and significantly reduce idler maintenance costs.
Idler roll seals are known in the art. Generally, such seals are of the labyrinth type, the contact type, or a combination of both. Labyrinth seals employ a tortuous network of passages between the contaminating environment and the idler roll bearing assembly. Contaminants can only infiltrate the bearing assembly by traversing the tortuous path. In contrast, contact seals employ a physical barrier placed in direct contact with the end cap of the idler roll to act as a shield between the bearing assembly and the infiltrating contaminants. Lastly, combination seals combine features of the labyrinth and contact seals to enhance the ability of the seal to deter entry of contaminants into the bearing assembly area. In all of these instances, however, either the seal is part of the inner workings of the idler roll, requiring expensive installation of the seal during roll manufacture, or the seal is externally applied directly to an existing roll, but only after time consuming disassembly of the roll from its bracket. Thus the need for an effective, inexpensive, durable, and easily fabricated and installed idler roll seal for retrofitting existing idlers and for installation on new idlers without the need for time consuming and costly alteration of the rolls.